Monocytes express at least two different classes of cell-type specific genes. One class, exemplified gy the M-CSF receptor gene, c-fms, is constitutively expressed and dependent upon the differentiated state. Another class, represented by the IL-1beta gene (il1b), is also generally monocyte-specific, but is only expressed immediately in response to a stimulation event that parallels the conversion of the resting monocyte to the activated monocyte/macrophage. Investigation of the il1b regulation mechanisms have revealed two distinct and separable regions of the gene that correspond to each of the two criteria, a cell type specific 143bp basal promoter and a signal-responsive upstream enhancer. The enhancer function depends upon the cooperative function of several broadly expressed signal-responsive transcription factors (e.g., C/EBPbeta, CREB, c-Jun, and NF- kappaB), including a novel STAT-like factor, whereas the 71 bp basal promoter appears to depend upon binding of one molecule of the mono-myeloid factor Spi-1/PU.1 (Spi-1), a factor that plays a central key role in monocyte development and cell type-specific gene expression. The functional interaction between the basal promoter and an enhancer requires a critical additional 73bp element that requires the binding of an additional Spi-1 molecule. This element is not required for enhancer-independent activity in the presence of IE2, a cytomegalovirus protein. IE2 appears to interact directly with the Spi-1 ETS domain. This region is found in all ETS proteins and mediates associations with a broad range of other proteins, modulating function in both partners. The object of this proposal is to elucidate the mechanism by which Spi-1 interacts with other proteins and integrates enhancer function into the core promoter and to attempt to clone the novel STAT-like factor that is activated in response to LPS, IL-1, and IL-6.